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Simplify SignExtend a little. 

Signed-off-by: Adrian Conlon <Adrian.conlon@gmail.com>
This commit is contained in:
Adrian Conlon 2019-08-15 22:45:56 +01:00
parent 9ca85428e0
commit c06f556669
1 changed files with 3 additions and 4 deletions
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7
EightBit/Processor.cs
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@ -42,10 +42,9 @@ namespace EightBit
// http://graphics.stanford.edu/~seander/bithacks.html#FixedSignExtend
public static sbyte SignExtend(int b, byte x)
{
var m = (byte)(1 << (b - 1)); // mask can be pre-computed if b is fixed
x = (byte)(x & ((1 << b) - 1)); // (Skip this if bits in x above position b are already zero.)
var result = (x ^ m) - m;
return (sbyte)result;
var m = Bit(b - 1); // mask can be pre-computed if b is fixed
x &= (byte)(Bit(b) - 1); // (Skip this if bits in x above position b are already zero.)
return (sbyte)((x ^ m) - m);
}
public static sbyte SignExtend(int b, int x) => SignExtend(b, (byte)x);